Solid free-form fabrication (SFF) is a designation for a group of processes that produce three dimensional shapes from additive formation steps. SFF does not implement any part-specific tooling. Instead, a three dimensional component is often produced from a graphical representation devised using computer-aided modeling (CAM). This computer representation may be, for example, a layer-by-layer slicing of the component shape into consecutive two dimensional layers, which can then be fed to control equipment to fabricate the part. Alternatively, the manufacturing process may be user controlled instead of computer controlled. Generally speaking, a component may be manufactured using SFF by successively building feedstock layers representing successive cross-sectional component slices. Although there are numerous SFF systems that use different components and feedstock materials to build a component, SFF systems can be broadly described as having an automated platform/positioner for receiving and supporting the feedstock layers during the manufacturing process, a feedstock supplying apparatus that directs the feedstock material to a predetermined region to build the feedstock layers, with the individual layers solidifying prior to deposition of the next layer. An energy source is directed toward the predetermined region. The energy from the energy source modifies the feedstock in a layer-by-layer fashion in the predetermined region to thereby manufacture the component as the successive layers are built onto each other.
One recent implementation of SFF is generally referred to as ion fusion formation (IFF). With IFF, a torch such as a plasma, gas tungsten arc, plasma arc welding, or other torch with an orifice is incorporated in conjunction with a stock feeding mechanism to direct molten feedstock to a targeted surface such as a base substrate or an in-process structure of previously-deposited feedstock. A component is built using IFF by applying small amounts of molten material only where needed in a plurality of deposition steps, resulting in net-shape or near-net-shape parts without the use of machining, molds, or mandrels. The deposition steps are typically performed in a layer-by-layer fashion wherein slices are taken through a three dimensional electronic model by a computer program. A positioner then directs the molten feedstock across each layer at a prescribed thickness.
There are also several other SFF process that may be used to manufacture a component. SFF processes can be sub-divided into subcategories such as additive manufacturing with further sub categories of direct metal deposition (DMD) and selective laser sintering (SLS) to name just a few. DMD is a process whereby metal is melted then placed where needed to build a three-dimensional part. SLS on the other hand spreads a layer of powder on a table then selectively fuses the appropriate portion to build a three-dimensional component. Typically, during the SFF process a desired shape is built in a chamber with inert gas or a vacuum to protect the liquid and solidified metal from oxidation. It would be an advantage to be able to build components especially large components with localized shielding to protect the deposit in lieu of a gas tight or vacuum tight chamber. However, most of the gas shields constructed for IFF systems are cylindrical shaped for use with relatively small components. These small cylindrical shaped shields effectively protect the top deposition layer of the workpiece being built, thereby enabling a sound interface with the next layer. These cylindrical shields are not effective in protecting the sides of the workpiece from oxidation. However, this current generation of all cylindrical shields has been effective because the limited oxidation on the sides of the workpiece is machined away subsequent to fabrication of the workpiece.
One of the greatest potential advantages but also a great challenge of SFF processes, and more particularly ion fusion formation (IFF) processes is that of achieving a net shape build or near net build, thereby reducing or eliminating the need for subsequent machining. As machining is reduced, the overall cost of the component is reduced. Thus, protecting of the sides form oxidation and therefore reduction of machining due to oxidation would be most beneficial. Accordingly, SFF systems, but most especially IFF may benefit from localized shielding for large structures, especially plate or plate like structures. Current localized shielding deigns do not cover sufficient area to protect the sides from oxidation. While these issues are most directly suited to IFF, any solutions could also be suited to other energy beam forms of SFF such as laser based systems, electron beam systems, or the like.
Hence, there is a need for a shielding structure that minimizes side aspect oxidation of a workpiece fabricated using solid free-form fabrication (SFF) processes.